3D printing, also known as additive manufacturing or additive layer manufacturing, is the construction of a three-dimensional object from a digital 3D model. The name additive manufacturing comes from the differentiation of 3D printing, which adds material layers upon each other to build an object, from the more traditional process of subtractive manufacturing, which removes material through milling, machining, carving, and shaping to create an object.
Traditionally, subtractive manufacturing has been used for high production volume manufacturing, while additive manufacturing has been reserved for prototyping and rapid tooling. However, the increased cost-effectiveness of additive manufacturing, the reduction of material waste, and the increased mainstream adoption of 3D printing systems has increased the use of additive manufacturing systems. These, along with the increased precision, repeatability, and material range of 3D printing, have increased the use of the technology for higher volume production.
In the case of most 3D printers, a user creates a design using computer aided design software or by scanning an object to print. Software translates the design into the printed layers and framework for the machine to follow. The plan is sent to the printer, which begins creating the object. The materials capable of being printed include polymers, metals, ceramics, foams, gels, and biomaterials.
Material extrusion printing, or fused filament fabrication, also known by the trademarked term "fused deposition modeling," is a 3D printing process using a continuous filament of a thermoplastic material. Through this method, filament is fed through a moving, heated printer extruder head and deposited on a growing work. Printers using this method use a computer to control the printed shape. And printers of this type layer the printed object one horizontal layer at a time before making a small vertical move to start the next layer. The extruder head speed can be controlled to start and stop deposition in order to form an interrupted plane without stringing or dribbling between sections. Fused filament fabrication is the more popular printing process (by number of machines) for hobbyist-grade 3D printing.
The fused deposition modeling technique was developed by S. Scott Crump, the co-founder of Stratasys, in 1988. The patent on the technology expired in 2009 and presented the beginning of people using the type of printing without paying rights to Stratasys. This allowed commercial, hobbyist, and open-source 3D printer applications to grow.
The materials capable of being extruded by fused filament fabrication machines include thermoplastics, such as acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), high-impact polystyrene (HIPS), thermoplastic polyurethane (TPU), and aliphatic polyamides (nylon).
Stereolithography (SLA), also known as optical fabrication, photo-solidification, VAT photopolymerisation, or resin printing, is a 3D printing technology that prints parts in a layer-by-layer fashion using photochemical processes. SLA uses light to cause chemical monomers and oligomers to cross-link and form polymers that, in turn, make the body of a three-dimensional solid. The process is fast and can produce almost any design, but can be cost prohibitive. The main fields of application include products in development, medical models, and computer hardware.
The materials used in SLA printing are referred to as resins and are thermoset polymers. These resin materials can be soft or hard, filled with secondary materials such as glass and ceramic, or imbued with mechanical properties such as heat deflection or impact resistance. In the post-process of SLA manufacturing, parts need to be removed from a support structure, and alcohol and water rinses are used to remove excess resin. At times, post processing can include scrubbing to remove additional material, and some processes use ultraviolet light for a post-cure process.
Stereolithography was first developed in the early 1980s by Hideo Kodama, who used ultraviolet light to cure photosensitive polymers. French inventors Alain Le Mehaute, Oliver de Witte, and Jean Claude Andre filed an early patent for technology that was later abandoned. The final patent, which gave the process the name "stereolithography," was filed by Chuck Hull in 1984 and granted in 1986. Chuck Hull later founded 3D Systems to commercialize the patented technology.
The powder bed fusion manufacturing process includes the printing techniques of direct metal laser sintering, electron beam melting, selective heat sintering (SLS), selective heat sintering, and selective laser melting (SLM). All methods use either a laser or an electron beam to melt and fuse material powder together. The methods involve spreading the powder material over previous layers, using either a roller or a blade while a hopper or reservoir provides fresh material supply. In all methods, a layer, typically 0.1 millimeters thick, of material is built over the platform and the laser or electron beam fuses new material in layers or cross-sections. Materials capable of being used in powder bed fusion manufacturing processes include nylon, stainless steel, titanium, aluminum, cobalt chrome, steel, and copper.
In direct metal laser sintering, metal powders are sintered layer by layer with a range of metals available.
In electron beam melting (EBM), layers are fused using an electron beam to melt metal powders. In the EBM process, a vacuum is required with a pressure of 1×10-5 mba, and electromagnetic coils are used to control the beam. The EBM process also produces better strength properties due to even temperature during fusion. These strength properties with the high quality and finish of the product suits it to manufacturing of parts for aerospace and medical applications.
In selective laser sintering (SLS), machines are made up of three components: a heat source, a method to control the heat source, and a mechanism to add new layers of materials. The SLS process requires no additional support structure for the product being printed. In the SLS chamber, nitrogen is often used to maximize the oxidation and end quality of the model. A cool-down period is also required to ensure high tolerance and quality of fusion. Some SLS machines monitor the temperatures layer by layer and adapt the power to improve quality. SLS processes use plastic powders, rather than metal powders used in direct metal laser sintering.
Selective heat sintering uses a heated thermal printhead to fuse powder material. Layers are added with a roller between fusion of layers. The use of a thermal printhead reduces the heat and power levels required for printing. Selective heat sintering systems use thermoplastic powders and require support materials in the process of printing. The process is often used to create concepts prototypes rather than structural components.
Selective laser melting (SLM) is similar to selective laser sintering, except it is faster while requiring the use of an inert gas and requiring higher energy use with poor overall energy efficiency. Through the process, a roller or blade is used to spread new layers of powder over previous layers. In cases when a blade is used, the blade is often vibrated to encourage a more even distribution of powder.
Material jetting, also known as multi-jet modeling, creates objects in a similar method to an inkjet printer. The process uses droplets to build a material on a support structure, while ultraviolight light or heat cures the droplets to create a 3D object. In the technique, droplets are selectively deposited on an X, Y, and Z axis controlled by computer and based on computer-aided designs. Common materials used in material jetting machines include polymers and waxes, due to their viscous nature that can form droplets. Overall, the materials suitable for use in material jetting machines are limited. And the parts printed through material jetting printers are mainly suitable for non-functional prototypes, as the printed parts often have poor mechanical properties.
The types of material jetting technologies include PolyJet technology, NanoParticle Jetting, and Drop On Demand. PolyJet technology jets thin layers of photopolymer material onto a build tray, in which each layer is cured by ultraviolet light. PolyJet technology was the first material jetting technology introduced. The PolyJet process was developed by Object and was later bought by Stratasys.
NanoParticle jetting technology was developed by XJet and uses a dispersion methodology to deposit solid nanopoarticles suspended in a liquid and jetted onto the build tray. In the system, two printheads and thousands of nozzles spray ultrafine drops that both build and support materials onto the build trays, while high temperature in the build area evaporates the liquid jacket around the nanoparticles. The remaining nanoparticles are sintered and the support material is removed, with a thin and smooth surfaced product capable of fine details remaining.
Drop on demand (DOD) technology is a process typically used for viscous materials, and consists of deposits tiny dots of material instead of continuous lines. The printers consist of two heads for each build and support material and are often used for make wax patterns for investment casting. In the printing process, wax material is printed in layers with the support material automatically laid down and eliminating the need for designers to create support structures. The finished part is placed in a liquid bath which dissolves the support material away.
Binder jetting is a manufacturing technique in which a binding liquid is selectively deposited to join powder material to form a 3D part. The process does not require heat during the printing process. Exon, an early developer of the binder jetting technique, uses furan binder, silicate binder, phenolic binder, and aqueous-based binder for their binder jetting printers. Regardless of binder, the process of a binder jetting printer sees the application of a layer of material powder, followed by a printhead depositing the binder adhesive on the powder where required until a 3D model is finished. The unbound powder remains until it is removed.
Binder jetting processes can manufacture in a range of different colors and in a range of metal, polymers, and ceramics. The two-material process allows for many different binder-powder combinations with various mechanical properties. However, often, through the use of specific binder materials, binder jetting printed materials are not always suitable for use as structural parts.
Sheet lamination is a process of building a 3D object by stacking and laminating thin sheets of material. The lamination method can be bonding, ultrasonic welding, or brazing while a final shape is achieved through laser cutting or CNC machining. Sheet lamination produces parts with the least additive resolution compared to other additive manufacturing processes; however, it is a low cost and offers fast manufacturing times from easily available low-cost material.
The materials involved in sheet lamination include paper, plastic, metal, and woven fiber composites. Forming methods include CNC milling, laser cutting, and aqua blasting. And the lamination techniques include adhesive bonding, thermal bonding, and ultrasonic welding. The process either follows a form then bond process, in which sheet material is cut into shape and then bonded layer on layer to create a 3D object. Or it follows a bond then form process, in which the material layers are bonded and then cut into the desired shape. Sheet lamination types, each offering some kind of variation of the above methods, can be categorized into seven types:
- Laminated object manufacturing (LOM)
- Selective lamination composite object manufacturing (SLCOM)
- Plastic sheet lamination (PSL)
- Computer-aided manufacturing of laminated engineering materials (CAM-LEM)
- Selective deposition lamination (SDL)
- Composite based additive manufacturing (CBAM)
- Ultrasonic additive manufacturing (UAM)
Directed energy deposition is an additive manufacturing process that forms 3D objects by melting material as it is deposited using focused thermal energy such as laser, electron beam, or plasma. Both energy source and the material feed nozzle are manipulated using a gantry system or robotic arm. Due to the nature of direct energy deposition, even though it is possible to create 3D objects from scratch, the process is generally used for adding to an existing part or repairing existing parts. Direct energy deposition systems are used in hybrid manufacturing, in which a substrate bed is moved to create complex shapes.
Direct energy deposition systems can be used to make metal, ceramic, and polymer parts, although they are primarily used to make metal parts. The types of systems include laser-based systems, such as Optomec's laser engineering net shape system, which uses a laser as the main energy source. An electron beam based system, such as Sciaky's electron beam additive manufacturing system, uses electron beams to melt the powdered material feedstock. And the plasma or electric arc based system, such as Wire's arc additive manufacturing process use electric arcs to melt wire.
The suitable materials for direct energy deposition systems include niobium, titanium and titanium alloys, inconel, stainless steels, hastelloy, aluminum alloy, tantalum, zinc alloy, tungsten, and copper-nickel alloys. Direct energy deposition systems are used in industries such as aerospace, defense, oil and gas, and the marine industry.
The applications for 3D printing are various across industries and for hobbyist uses with the introduction of lower cost printing technology.
3D printing is being explored as a construction method that reduces the costs of on-site construction and time-to-build of a home. The application of 3D printing in home construction has been explored as an affordable housing solution for urban areas.
Additive manufacturing systems are capable of producing lightweight parts with complex geometric designs useful for the aerospace industry. In 2013, NASA tested SLM-printed rocket injector during a hot fire test generating 20,000 pounds of thrust. In 2015, the FAA cleared 3D-printed parts for use in commercial jet engines. In the 2017 Paris Air Show, the Boeing 787 displayed FAA-certified structural parts fabricated from 3D printing of titanium wire.
The automotive industry has used 3D printing processes for rapid prototyping. As manufacturing techniques have advanced, 3D printing has been used for developing automotive parts. This includes the McLaren Formula 1 racing team using 3D printed parts in their race cars, including a rear wing replacement that took ten days to produce using 3D printers, instead of the five weeks subtractive manufacturing can take. In 2014, Koenigsegg, Swedish supercar manufacturer, used 3D printing for many components. Most of the manufacturing processes extend to the bodywork and related elements, but do not extend to the powertrain.
Additive manufacturing has been used in the healthcare industry to produce medical items and prosthetics. This has included medical device manufacturing company Stryker using additive manufacturing technology to create surgical implants for patients suffering from bone cancer. A clinical study done by the New York University School of Medicine is looking into the use of patient-specific, multi-colored kidney cancer models and whether they can effectively assist surgeons with pre-operative assessments.
There have been studies into the viability of 3D bio-printing for use in tissue engineering applications, including the printing of organs and body parts. In the process, layers of living cells are deposited onto a gel medium or sugar matrix to build a three-dimensional structure, including vascular systems. In May 2018, a 3D printing system was used for a kidney transplant to save a three-year-old boy.
In the pharmaceutical industry, 3D printing systems are being used by researchers as a new way to develop formulations of materials and compounds not possible with conventional techniques such as tableting or cast-molding. One of the possible uses of 3D printing in pharmaceuticals is to print personalized dosages to better target patient needs.
In the clothing and fashion industry, designers and manufacturers have experimented with 3D printed clothing items, including Nike using 3D printing to prototype and manufacture their 2012 Vapor Laser Talon football shoes and New Balance 3D manufacturing custom-fit shoes for athletes.
In 3D printing for shoes, the additive manufacturing techniques offers a chance for creators and designers in the fashion industry to create designs and collections with shapes or designs that could be otherwise unable to create in subtractive manufacturing methods. As well, there are many projects launching to develop new speakers, futuristic lightweight footwear, and customer printed shoes for specific athletes.
Additive manufacturing systems, or analogues, are also being used in the manufacturing of food. The foods printed have included chocolate, candy, crackers, pasta, and pizza. NASA has pursued research into the technology to reduce food waste and design foods to fit astronauts' dietary needs. And in 2018, Giuseppe Scionti developed technology to generate fibrous plant-based meat analogues using a custom-built 3D bioprinter.
Often 3D printing in foods describes an additive manufacturing process, such as an automated pizza vending machine that is capable of extruding dough, topping the dough with tomato sauce and cheese, and sending that to an oven. Food can, especially in the case of viscous foods, be printed fairly easily. 3D printing has been used for decorating and deserts where the accuracy of the printer can create complex designs. However, in the case of other types of food, 3D printing can be more restrictive. As well, in the case of 3D printing new or novel foods, the technology is further behind its peers, as the technology can be prohibitively expensive and often is not scalable.
Additive manufacturing has been used in the firearms industry to offer a new manufacturing method for established companies, and has produced possibilities for the do-it-yourself manufacturing of firearms.
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